In-line centrifugal fan

ABSTRACT

In an in-line centrifugal fan having an annular centrifugal impeller mounted for rotation within a tubular housing, a plurality of independent axial-type impeller blades mounted for rotation with the centrifugal impeller and juxtaposed with the path of air discharged radially from the centrifugal impeller so as to draw such air into the axial-type blades and direct the air in an axial direction toward the outlet of the fan.

United States Patent Benoit Mar. 21, 1972 54] IN.LINE CENTRIFUGAL FAN FOREIGN PATENTS OR APPLICATIONS [72] Inventor: Remi A. Benoit, 27 Pinewood Drive, Nep- 873,190 4/1953 Germany ..4l/ 143 tune, NJ. 07755 443,620 3/1936 Great Britain ...4l5/143 833,100 3/1952 Germany ..415/l43 22 Fl d. N .30, 1970 I 1 115,129 12/1955 Germany ..415/143 [21] Appl. No.: 93,600 466,375 /1951 Italy ...4l5/l43 60,846 7/1912 Switzerland ..4l5/l43 I52] U.S.CI. AIS/143,4l5/219,417/423,

415/215 Primary ExaminerHenry F. Raduazo 51 1 1111. C1 ..F04d /16, F04d 25/02, F04d 29/40 Attorney-Samuelson & Jacob [58] FleldoISearch ..4l5/143,2l9,2l5;4l7/204,

417/423 ABSTRACT In an in-line centrifugal fan having an annular centrifugal im- [56] References cued peller mounted for rotation within a tubular housing, a plurali- UNITED STATES PATENTS ty of independent axial-type impeller blades mounted for rotation with the centrifugal im eller and juxtaposed with the path P 1,738,210 12/1929 Sargent ..416/203 of discharged radially from the centrifugal impeller so as to 3 1 6/1943 9 7 draw such air into the axial-type blades and direct the air in an 12; i 2 1 axial direction toward the outlet of the fan. ar son.. 1,341,882 6/1920 Criqui ..415/204 8 Claims, 5 Drawing Figures a0 Q6 :1 qa 1 ./-'64 42 1 62 x as 84 I J a r a E 94 82 T. 62 3 12 9 a 0 I7Q== 14 i-"vo 4 6 .2

Patented March 21, m2 mmss 2 Sheets-Sheet 2 INVEN F? NOIT BY R A HTTOR Y5 IN-LINE CENTRIFUGAL FAN The present invention relates generally to fans, and pertains, more specifically, to in-line centrifugal fans of the type in which an annular centrifugal impeller is mounted for rotation within a tubular housing having a fluid inlet and a fluid outlet located axially opposite one another.

In-line tubular fans are commonly used in air handling and distribution systems where such fans can be installed as a segment of the ductwork of such systems, thereby enabling a saving in space and simplifying the configuration of the ducts themselves.

Because of the prevalence of scroll-type centrifugal fans constructed in many different sizes for use in such systems, a wide variety of annular centrifugal impellers of the type employed in scroll centrifugal fans are commercially available. It has been suggested that relatively inexpensive in-line tubular fans can be constructed by merely placing a commercially available annular centrifugal impeller within a tubular housing, rather than within the scroll housing for which such an impeller is designed.

While such an arrangement allows economical fabrication, these fans suffer from adverse effects arising out of the fact that the air discharged from the impeller is directed radially toward the wall of the housing and must turn 90 to continue on an axial path through the fan housing. Actually, the radial discharge from the impeller becomes divided into two diverging flow paths which are in substantially opposite axial directions. A substantially larger portion of the discharged air is directed radially toward the housing and then moves axially in a direction away from the inlet; however, a smaller, but still substantial, quantity of air moves in an opposite axial direction toward the inlet side of the impeller. The impact of the radial blast of air against the housing, together with the separation of the air flow along paths extending in opposite axial directions results in a turbulent condition producing costly losses of energy with a concomitant loss of efficiency. Furthermore, such turbulence creates undue noise. Additionally, the air which is directed axially back toward the inlet side of the impeller can find its way back to the inlet of the impeller, thus causing recirculation of air through the fan. Such a recirculation condition results in an additional loss in efficiency.

It has been suggested that auxiliary blades be employed in the form of stator blades in the annular space between the centrifugal impeller and the tubular housing in order to direct radially discharged air toward the housing outlet and to deter the flow of air back toward the inlet. While such measures have met with moderate success, they require a relatively elaborate housing construction which may not necessarily be justified by the advantages attained.

It has been found that the above enumerated difficulties which arise from the use ofa centrifugal impeller in a tubular housing can be effectively reduced or eliminated while other advantages are attained by simply adding a plurality of independent axial-type impeller blades extending into the annular space between the centrifugal impeller and the housing just downstream of the air discharged radially from the centrifugal impeller. These blades can be rotated along with the centrifugal impeller to divert the radially discharged air into the desired axial direction.

It is therefore an important object of the invention to provide an in-line fan construction in which an annular centrifugal impeller may be utilized with greater effectiveness than before.

Another object of the invention is to provide an in-line centrifugal fan with relatively inexpensive yet effective means for reducing turbulence and noise within the fan housing and for increasing the efficiency of operation of the fan.

Still another object of the invention is to provide means by which commercially available centrifugal impellers constructed for use in scroll-type fans may be adapted conveniently for use in tubular in-line fans with minimum complexity and expense and with good performance characteristics.

A further object of the invention is to provide an in-line centrifugal fan which is relatively inexpensive to fabricate and which exhibits relatively high efficiency as well as exemplary performance characteristics over a wide range of operating conditions.

The above objects, as well as still further objects and advantages, are attained by the invention which may be described briefly as an in-line centrifugal fan comprising a tubular housing having a longitudinal axis, a fluid inlet and an axially opposite fluid outlet, an annular centrifugal impeller mounted for rotation within the housing about an axis of rotation parallel with the longitudinal axis of the housing and in cluding a plurality of radial-type impeller blades for drawing fluid axially from the inlet adjacent the radially inner leading edges of the blades and discharging the fluid along a path extending radially from the radially outer trailing edges of the blades toward the housing, and a plurality of independent axialtype impeller blades mounted for rotation within the housing and extending radially between the trailing edges of the radialtype impeller blades and the housing, with the leading edges of the axial-type blades in juxtaposed relationship with the path of the radially discharged fluid between the trailing edges of the radial-type impeller blades and the housing and located axially between the radial-type impeller blades and the outlet of the housing such that the fluid discharged from the radialtype blades will be drawn into the axial-type blades and discharged from the axial-type blades axially toward the outlet.

The invention will be more fully understood while still further objects and advantages will become apparent in the following detailed description of an embodiment of the invention illustrated in the accompanying drawing, in which:

FIG. 1 is a side elevational view of an in-line centrifugal fan constructed in accordance with the invention and shown installed within a duct;

FIG. 2 is an enlarged longitudinal view of the fan of FIG. 1 with the housing sectioned along line 22 of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of the fan taken along line 3-3 of FIG. 1;

FIG. 4 is a lateral cross-sectional view, slightly reduced, taken along line 44 of FIG. 3; and

FIG. 5 is a lateral cross-sectional view, slightly reduced, taken along line 5-5 of FIG. 3.

Referring now to the drawing, and especially to FIG. 1 thereof, an in-line centrifugal fan constructed in accordance with the invention is indicated generally at 10 and is shown installed within a duct 12 of a fluid distribution system in this instance, the fluid being air. The external housing 14 of the fan 10 is cylindrical and matches the cylindrical configuration of the duct 12. In the illustrated embodiment, a pair of radially extending opposite end flanges l6 and 18 of the housing 14 are affixed to corresponding complementary flanges 20 and 22 of the ductwork so that the fan 10 is mounted in alignment with the confronting portions 24 and 26 of the duct 12 hence, the appellation in-line in the description of the fan 1 Turning now to FIGS. 2 and 3, fan 10 is seen to have a forward or inlet end 30 where there is located an inlet funnel or cone 32 which directs the incoming air to the inlet or eye 34 of a centrifugal impeller 36. The centrifugal impeller 36 is of the type commonly found in commercially available scroll-type fans and has a generally annular configuration which includes a plurality of radial-type impeller blades 38 having their leading edges 40 adjacent the eye 34, or the inside diameter of the annular configuration, and their trailing edges 42 located adjacent the outside diameter of the annular configuration (see FIG. 4). The blades 38 are backwardly inclined; that is, the trailing edge 42 of each blade follows behind the leading edge 40 of the blade, considering the direction of rotation of the impeller (see FIG. 4), as opposed to forwardly inclined blading where the trailing edge of each blade is located ahead of the leading edge of the blade, or purely radial blading where each blade follows a radius of the impeller so that neither one of the leading or trailing edges is ahead of or behind of the other of the edges. The radial-type blades 38 extend axially from a rear disk 44 to a forward shroud 46.

The rear disk 44 is affixed to a hub 48 which, in turn, is mounted for rotation with a drive shaft 50 by means of a key 52. The drive shaft 50 is journaled for rotation within a pair of bearing blocks 54 and 56 mounted upon corresponding lateral members 58 and 60 which are fixed in place within a cylindrical shell 62 supported within the housing 14 by means ofa plurality of support struts, in this instance the struts being in the form of vanes 64 extending radially between the housing 14 and the shell 62 (see FIG. The drive shaft extends axially along the longitudinal central axis of the fan such that the impeller 36, the shell 62, and the housing 14 are all located coaxially with respect to the central axis.

A drive motor 66 is mounted upon the exterior of the housing 14 and carries a drive pulley 68 engaging a drive belt 70 which passes through a sleeve 72 into the shell 62 and is engaged with a driven pulley 74 affixed to the drive shaft 50. Thus, upon operation of the drive motor 66, the drive shaft 50 is rotated to rotate the centrifugal impeller 367 The impeller 36 is rotated in the direction indicated by the arrows in FIGS. 2, 3 and 4 and air is drawn through the inlet end of the housing and guided by the inlet cone 32 to the eye 34 of the impeller 36. The air is then driven by the radial-type impeller blades 38 in a radial direction to be discharged from the impeller 36 into the annular space 76 between the outer periphery of the impeller 36 and the housing 14, the discharged air tending to follow a radial path from the external periphery of the impeller toward the housing. Such radially directed air will have the tendency to continue its travel in a radial direction and, in the absence of any further structure, would strike the interior of the housing 14, so that the flow of air would be divided into two diverging flow paths moving in substantially opposite axial directions. Since a forward flow path would give rise to an accumulation of air in the zone behind the inlet cone 32, most of the radially directed air would tend to follow a rearward flow path passing along the annular chamber 78 between the housing 14 and the shell 62 and out of the fan 10 through the outlet 80 at the rear thereof. It has been found that the impact of such a radial blast of air against the housing, together with the separation of the air flow into opposite axial directions results in a very turbulent condition producing costly losses of energy and resulting in a loss of efficiency. In addition, such turbulence creates undue noise. Furthermore, although a close running fit is provided between the inside end 82 of the inlet cone 32 and the overlapping end 84 of the shroud 46, such a fit is not air-tight and, by virtue of the pressure differential across the space 86 between the end 82 of the inlet cone and the overlapping end 84 of the shroud, a significant quantity of air can pass from behind the inlet cone through the space 86 to return to the eye 34 of the impeller 36, thereby allowing recirculation of air through the fan 10, Such recirculation results in an additional loss in efficien- In order to reduce to a minimum all such turbulence, recirculation and concomitant deleterious effects, fan 10 is provided with a plurality of axial-type impeller blades 90 mounted for rotation within the housing 14 and extending into the annular chamber 78 immediately toward the rear, or downstream, of the path of the air discharged from the centrifugal impeller 36. Thus, axial-type impeller blades 90 are affixed to an impeller wheel 92 which is mounted upon the drive shaft 50 and rotates therewith by virtue of a key 94. It has been found that by placing a plurality of such axial-type impeller blades at the downstream end of the centrifugal impeller 36 with the axial blading extending to a reasonably close fit with the inside wall of the tubular housing 14, the radial blast of air against the housing is substantially reduced, the air being directed in unobstructed free flow into a rearward axial path, and consequently undesirable turbulence is eliminated. In addition, the separation of the air flow into opposite axial directions of flow is essentially eliminated, resulting in a reduction of the leakage of air through the space 86 between the inlet cone 32 and the impeller shroud 46. It has also been observed that the inclusion of such axial-type blading enables an increase in the volume of air delivered by the fan, and an increase in the pressure developed by the fan. The resulting increase in performance can be produced with lower horsepower than would ordinarily be anticipated by the use ofa centrifugal impeller combined with axial-type blading; consequently, relatively high efficiencies and quieter operation are attained. In addition, fans constructed in accordance with the invention exhibit a constantly rising pressure characteristic in the entire range of air delivery from wide open to no delivery at all, without the characteristic flattening offin pressure which is found in fans employing centrifugal impellers without supplemental axial blades. This rising pressure characteristic increases the range of application of fans constructed in accordance with the invention. Thus, the relatively simple expedient of adding a plurality of independent axialtype blades to a centrifugal impeller within a tubular housing attains desirable improvements in an in-line centrifugal fan.

It has also been found that where supplemental axial blades are employed, the number of recovery vanes on the discharge side of the impeller may be reduced; hence, whereas it would be expected that a fan of the type illustrated would require as many as 16 to 18 recovery vanes, it has been demonstrated that fans constructed in accordance with the invention require only about 25 percent of that number. Thus, fan 10 is shown with only four vanes 64.

In view of the above characteristics of fans constructed in accordance with the invention, such fans may be utilized at decreased operating speeds while producing the same air volume and pressure with substantially lower horsepower and substantially quieter operation than fans of comparable dimensions constructed without the supplementary axial blading. Conversely, a smaller fan constructed in accordance with the invention may be used to give the same volume and pressure at essentially the same speed, but with betterefficiency and quieter operation than with a larger fan which does not use supplementary axial blading.

It is noted that in the illustrated embodiment of the invention, the axial-type impeller blades 90 are mounted upon an impeller wheel 92 which is not an integral part of the centrifugal impeller 36. In this manner a standard, commercially available centrifugal impeller 36 may be utilized in the fan 10 without modification of the centrifugal impeller 36 and without supplementary structures in the housing 14. However, the same advantages as described above may be attained by affixing independent axial-type impeller blades directly to the centrifugal impeller itself. In such an instance, the mechanical construction of the fan may differ from that of the disclosed embodiment, but the location of the axial-type impeller blades with respect to the radial-type impeller blades will be the same; that is, the axial-type impeller blades 90 extend radially between the trailing edges 42 of the radial-type impeller blades 38 and the housing 14 with the leading edges 96 of the axial-type blades in juxtaposed relationship with the path of the radially discharged air between the trailing edges 42 of the radial-type impeller blades 38 and the housing 14 and located axially between the radial-type impeller blades 38 and the outlet of the housing 14 such that the air discharged from the radial-type blades 38 will be drawn into the axial-type blades and discharged from the axial-type blades axially toward the outlet 80. More complex mechanical configurations are available; for example, under certain circumstances it may be desirable to rotate the axial impeller wheel 92 independent of the rotation of the centrifugal impeller 36, and even in a direction of rotation opposite to the direction of rotation of the centrifugal impeller.

From the standpoint of efficiency and effectiveness, it has been found advantageous to employ a number of axial-type impeller blades 90 equal in number to the number of radialtype impeller blades 38 in the centrifugal impeller 36 and to locate the axial-type blades with respect to the radial-type blades such that the leading edges 96 of the axial-type blades are located circumferentially midway between the circumferential location of the trailing edges 42 of the radial-type blades, as illustrated in FIG. 4.

The pitch angle of the axial-type impeller blades 90 is dependent upon the particular configuration of the centrifugal impeller 36, the speed at which the impeller 36 will be rotated and the volume and pressure of air to be delivered at the outlet 80. Since some of these parameters may vary from fan to fan, or from installation to installation, it may be advantageous to mount the axial-type impeller blades 90 upon the impeller wheel 92 in such a manner that each blade may be adjusted to one of a plurality of pitch angles. Various mechanisms are available to attain a variable pitch mounting of the impeller blades 90 and may be used to increase the flexibility of operation of a particular fan constructed in accordance with the invention.

It is to be understood that the above detailed description of an embodiment of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as set forth in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An in-line centrifugal fan comprising:

a generally cylindrical tubular housing having a central longitudinal axis, a fluid inlet at a forward end of the housing and an axially opposite fluid outlet at the rearward end of the housing;

an annular centrifugal impeller mounted for rotation about an axis of rotation concentric with the central axis of the housing, the impeller being of the type which includes a plurality of radial-type impeller blades arranged in an annular configuration around a central eye and including radially inner leading edges adjacent the eye and radially outer trailing edges adjacent the outside diameter of the impeller, said outside diameter of the impeller at the trailing edges of the radial-type impeller blades being smaller than the inside diameter of the housing such that there is an annular space between said trailing edges and the housing, and a shroud along the forward ends of the radial-type impeller blades, whereby fluid will be drawn by the impeller blades from the eye adjacent the radially leading edges of the blades and will be discharged along a radial path extending from the radially outer trailing edges of the blades, into the annular space, and toward the housing;

means for conducting fluid from the inlet of the housing to the eye of the impeller, said conducting means being located forward of said annular space and establishing a zone within said housing axially forward of said annular space; and

a plurality of independent axial-type impeller blades mounted for rotation within the housing rearward of the radial-type impeller blades and extending radially between said outside diameter of the centrifugal impeller and said inside diameter of the housing such that the leading edges of the axial-type impeller blades are juxtaposed with said annular space, to the rear of said annular space, whereby the fluid discharged from the radial-type blades into the annular space will be drawn into the axial-type blades so that the fluid will pass in unobstructed free flow from said radial path into an axial path and thereby directed away from said zone to be discharged from the axial-type blades axially toward the outlet of the housing.

2. The in-line centrifugal fan of claim 1 wherein the radialtype impeller blades are backwardly inclined.

3. The in-line centrifugal fan of claim 1 wherein the axialtype impeller blades are mounted for rotation in the same direction as the rotation of the centrifugal impeller.

4. The in-line centrifugal fan of claim 1 wherein the radialtype impeller blades are backwardly inclined and the axialtype impeller blades are mounted for rotation in the same direction as the rotation of the centrifugal impeller.

5. The ln-line centrifugal fan of claim 1 wherein the axialtype impeller blades are mounted for rotation with the centrifugal impeller.

6. The in-line centrifugal fan of claim 5 wherein the radialtype impeller blades are spaced circumferentially equidistant from one another, the number of axial-type impeller blades is equal to the number of radial-type impeller blades, and the leading edges of the axial-type blades are located circum ferentially midway between the circumferential location of the trailing edges of the radial-type blades.

7. The in-line centrifugal fan of claim 1 wherein the radialtype impeller blades are backwardly inclined and the axialtype impeller blades are mounted for rotation with the centrifugal impeller.

8. The in-line centrifugal fan of claim 7 wherein the radialtype impeller blades are circumferentially equidistant from one another, the number of axial-type impeller blades is equal to the number of radial-type impeller blades and the leading edges of the axial-type blades are located circumferentially midway between the circumferential location of the trailing edges of the radial-type blades. 

1. An in-line centrifugal fan comprising: a generally cylindrical tubular housing having a central longitudinal axis, a fluid inlet at a forward end of the housing and an axially opposite fluid outlet at the rearward end of the housing; an annular centrifugal impeller mounted for rotation about an axis of rotation concentric with the central axis of the housing, the impeller beiNg of the type which includes a plurality of radial-type impeller blades arranged in an annular configuration around a central eye and including radially inner leading edges adjacent the eye and radially outer trailing edges adjacent the outside diameter of the impeller, said outside diameter of the impeller at the trailing edges of the radial-type impeller blades being smaller than the inside diameter of the housing such that there is an annular space between said trailing edges and the housing, and a shroud along the forward ends of the radial-type impeller blades, whereby fluid will be drawn by the impeller blades from the eye adjacent the radially leading edges of the blades and will be discharged along a radial path extending from the radially outer trailing edges of the blades, into the annular space, and toward the housing; means for conducting fluid from the inlet of the housing to the eye of the impeller, said conducting means being located forward of said annular space and establishing a zone within said housing axially forward of said annular space; and a plurality of independent axial-type impeller blades mounted for rotation within the housing rearward of the radial-type impeller blades and extending radially between said outside diameter of the centrifugal impeller and said inside diameter of the housing such that the leading edges of the axial-type impeller blades are juxtaposed with said annular space, to the rear of said annular space, whereby the fluid discharged from the radial-type blades into the annular space will be drawn into the axial-type blades so that the fluid will pass in unobstructed free flow from said radial path into an axial path and thereby directed away from said zone to be discharged from the axial-type blades axially toward the outlet of the housing.
 2. The in-line centrifugal fan of claim 1 wherein the radial-type impeller blades are backwardly inclined.
 3. The in-line centrifugal fan of claim 1 wherein the axial-type impeller blades are mounted for rotation in the same direction as the rotation of the centrifugal impeller.
 4. The in-line centrifugal fan of claim 1 wherein the radial-type impeller blades are backwardly inclined and the axial-type impeller blades are mounted for rotation in the same direction as the rotation of the centrifugal impeller.
 5. The in-line centrifugal fan of claim 1 wherein the axial-type impeller blades are mounted for rotation with the centrifugal impeller.
 6. The in-line centrifugal fan of claim 5 wherein the radial-type impeller blades are spaced circumferentially equidistant from one another, the number of axial-type impeller blades is equal to the number of radial-type impeller blades, and the leading edges of the axial-type blades are located circumferentially midway between the circumferential location of the trailing edges of the radial-type blades.
 7. The in-line centrifugal fan of claim 1 wherein the radial-type impeller blades are backwardly inclined and the axial-type impeller blades are mounted for rotation with the centrifugal impeller.
 8. The in-line centrifugal fan of claim 7 wherein the radial-type impeller blades are circumferentially equidistant from one another, the number of axial-type impeller blades is equal to the number of radial-type impeller blades and the leading edges of the axial-type blades are located circumferentially midway between the circumferential location of the trailing edges of the radial-type blades. 